sazabi:
Again, the reason I want to use Accelstepper is that I need to control 2 steppers simultaneously by 2 pots.
Let's go back to the very basics.
Describe what you want to achieve. Maybe there is no need to use any library - especially if you just want the motors to get up to some speed and stay at that speed for a long time.
Most stepper libraries are designed for making motors move a specific number of steps and that does not seem to be what you need.
Have a look at these links
Stepper Motor Basics
Simple Stepper Code
and it is not difficult to write your own acceleration code.
...R